Organic Chemistry of Explosives

Addition of nitric acid, nitrogen oxides 3

centres which are only nitrated with difficulty. With increased temperature these reactions

become less selective; at temperatures of 410–430◦C hydrocarbons often yield a complex

mixture of products. At these temperatures alkyl chain fission occurs and nitroalkanes of

shorter chain length are obtained along with oxidation products. An example is given by Levy

and Rose^16 who nitrated propane with nitrogen dioxide at 360◦C under 10 atmospheres of

pressure and obtained a 75–80 % yield of a mixture containing: 20–25 % nitromethane, 5–10 %

nitroethane, 45–55 % 2-nitropropane, 20 % 1-nitropropane and 1 % 2,2-dinitropropane.

The nitration of moderate to high molecular weight alkane substrates results in very complex

product mixtures. Consequently, these reactions are only of industrial importance if the mixture

of nitroalkane products is separable by distillation. Polynitroalkanes can be observed from the

nitration of moderate to high molecular weight alkane substrates with nitrogen dioxide. The

nitration of aliphatic hydrocarbons has been the subject of several reviews.^15 ,^17

Both nitric acid and nitrogen dioxide, in the liquid and vapour phase, have been used for the

nitration of the alkyl side chains of various alkyl-substituted aromatics without affecting the

aromatic nucleus.^13 ,^18 Thus, treatment of ethylbenzene with nitric acid of 12.5 % concentration

in a sealed tube at 105–108◦C is reported to generate a 44 % yield of phenylnitroethane.^13 The

nitration of toluene with nitrogen dioxide at a temperature between 20–95◦C yields a mixture

of phenylnitromethane and phenyldinitromethane with the proportion of the latter increasing

with reaction temperature.^18

The nitration of aliphatic hydrocarbons with dinitrogen pentoxide^19 and nitronium salts^20

has been described. Topchiev^21 gives an extensive discussion of works related to hydrocarbon

nitration conducted prior to 1956.

1.4 ADDITION OF NITRIC ACID, NITROGEN OXIDES AND

RELATED COMPOUNDS TO UNSATURATED BONDS

1.4.1 Nitric acid and its mixtures

CC

2

70 % HNO 3 , 40 °C

25 %

NO 2

H 3 C CH 3

H

NO 2 NO 2

NO 2

CH 3 CH 3

1

H

Figure 1.2

Alkenes can react with nitric acid, either neat or in a chlorinated solvent, to give a mix-

ture of compounds, including:vic-dinitroalkane,β-nitro-nitrate ester,vic-dinitrate ester,

β-nitroalcohol, and nitroalkene products.^21 –^26 Cyclohexene reacts with 70 % nitric acid to yield

a mixture of 1,2-dinitrocyclohexane and 2-nitrocyclohexanol nitrate.^23 Frankel and Klager^24

investigated the reactions of several alkenes with 70 % nitric acid, but only in the case of

2-nitro-2-butene (1) was a product identified, namely, 2,2,3-trinitrobutane (2).

H

CH 3

H 3 C H 3 C

H 3 C H 3 C

NO 2

CH 3

fuming HNO 3

20 %

43

Figure 1.3